This chronic skin disease isn’t easy to ignore: Its raised red patches covered with silvery scales itch (fittingly, “psoriasis” comes from the Greek for “itch”). Your self-image may suffer if it spreads. Psoriasis occurs when production of new skin cells outpaces the rate at which old ones are shed. As a result, live cells accumulate in raised areas covered with whitish flakes of immature skin cells (or plaques). Researchers say this rapid cell turnover relates to an inherited immune system disorder that can be activated by stress, cold weather, infection, or an abrasion.